Low nox burner for a water heater

ABSTRACT

A low NOx burner includes an upper plate and a lower plate joined together. A chamber is defined between an upper inner portion and a lower inner portion. The peaks of upper and lower scalloped ridges are in contact such that multiple ports are defined. The ports extend radially outward from the chamber. The chamber is adapted to receive a fuel/air mixture through a fuel/air intake opening. The ports permit a flow of the fuel/air mixture from the chamber for combustion to create a diffuse flame. An intermediate portion is positioned such that the flame attaches to the intermediate portion. The intermediate portion and a trough are arranged such that flame is directed downwards to the trough from the intermediate portion and attaches to the trough. An outer rim is positioned and angled to attach the flame to the trough and to direct the flame upwards from the trough.

RELATED APPLICATIONS

This application claims priority to co-pending U.S. Provisional PatentApplication No. 61/320,131 filed on Apr. 1, 2010, the entire content ofwhich is incorporated herein by reference.

BACKGROUND

The present invention relates to low NOx burners, and more particularlyto low NOx burners for water heaters.

Nitrogen oxides (NOx) are generated by high temperature flames duringcombustion. A low NOx burner reduces the amount of NOx formed duringcombustion. A low NOx burner for a water heater is typically defined asburner producing NOx in amounts no greater than 40 Ng/J.

SUMMARY

In one embodiment, the invention provides a low NOx burner including anupper plate and a lower plate. The upper plate defines an upper plateaxis and includes an inner upper portion, an upper scalloped ridgesurrounding the upper inner portion, and a lip surrounding the upperscalloped ridge. The upper inner portion extends radially outward afirst radial distance from the upper plate axis to the upper scallopedridge. The upper scalloped ridge defines peaks and valleys and has anupper portion. The lip angles radially outward and downward from theupper portion of the upper scalloped ridge and defines an outercircumferential edge of the upper plate. The lower plate defines a lowerplate axis and includes a lower inner portion, a lower scalloped ridgesurrounding the lower inner portion, an exit portion surrounding thelower scalloped ridge, an intermediate portion surrounding the exitportion, a trough surrounding the intermediate portion, and an outer rimsurrounding the trough. The inner portion has a fuel/air intake openingand extends radially outward the first radial distance from the lowerplate axis to the lower scalloped ridge. The lower scalloped ridgedefines peaks and valleys and has a lower portion. The exit portionangles radially outward and downward from the lower portion of the lowerscalloped ridge. The intermediate portion extends from the exit portionto a distal end at a second radial distance. The second radial distanceis greater than the first radial distance. The trough is below andradially outward of the intermediate portion. The outer rim includes anouter circumferential edge of the lower plate. The upper scalloped ridgeand the lower scalloped ridge are joined together so that the upperplate axis and the lower plate axis are collinear. A chamber is definedbetween the upper inner portion and the lower inner portion. The peaksof the upper and lower scalloped ridges are in contact such thatmultiple ports are defined between the valleys of the upper and lowerscalloped ridges. The ports extend radially outward from the chamberthrough the scalloped ridges. The chamber is adapted to receive afuel/air mixture through the fuel/air intake opening. The ports areadapted to permit a flow of the fuel/air mixture from the chamber forcombustion to create a diffuse flame. The intermediate portion ispositioned such that the flame attaches to the intermediate portion. Theintermediate portion and trough are arranged such that flame is directeddownwards to the trough from the intermediate portion and attaches tothe trough. The outer rim is positioned and angled to attach the flameto the trough and to direct the flame upwards from the trough.

In another embodiment, the invention provides a low NOx burner includingan upper plate and a lower plate. The upper plate defines an upper plateaxis and includes an inner upper portion, an upper scalloped ridgesurrounding the upper inner portion, and a lip surrounding the upperscalloped ridge. The upper inner portion extends radially outward afirst radial distance from the upper plate axis to the upper scallopedridge. The upper scalloped ridge defines peaks and valleys and has anupper portion. The lip angles radially outward and downward from theupper portion of the upper scalloped ridge and defines an outercircumferential edge of the upper plate. The lower plate defines a lowerplate axis and includes a lower inner portion, a lower scalloped ridgesurrounding the lower inner portion, an exit portion surrounding thelower scalloped ridge, an intermediate portion surrounding the exitportion, and an outer rim surrounding the intermediate portion. Theinner portion has a fuel/air intake opening and extends radially outwardthe first radial distance from the lower plate axis to the lowerscalloped ridge. The lower scalloped ridge defines peaks and valleys andhas a lower portion. The exit portion angles radially outward anddownward from the lower portion of the lower scalloped ridge. Theintermediate portion extends from the exit portion to a distal end at asecond radial distance. The second radial distance is greater than thefirst radial distance. The outer rim includes an outer circumferentialedge of the lower plate. The upper scalloped ridge and the lowerscalloped ridge are joined together so that the upper plate axis and thelower plate axis are collinear. A chamber is defined between the upperinner portion and the lower inner portion. The peaks of the upper andlower scalloped ridges are in contact such that multiple ports aredefined between the valleys of the upper and lower scalloped ridges. Theports extend radially outward from the chamber through the scallopedridges. The chamber is adapted to receive a fuel/air mixture through thefuel/air intake opening. The ports are adapted to permit a flow of thefuel/air mixture from the chamber for combustion to create a diffuseflame. The intermediate portion is positioned such that the flameattaches to the intermediate portion. The outer rim is positioned andangled to attach the flame to the lower plate and to direct the flameupwards from the lower plate.

In another embodiment, the invention provides a method of operating alow NOx burner. The method includes the step of providing a low NOxburner including an upper plate having an outer diameter and a lowerplate having an outer rim and an outer diameter, the plates joinedtogether to define a chamber and multiple ports formed between theplates, the ports extending radially outward from the chamber, and theouter diameter of the upper plate being less than the outer diameter ofthe lower plate. The method also including the steps of providing afuel/air mixture to the chamber, directing the fuel/air mixture throughthe ports, combusting the fuel/air mixture to create a flame, anddirecting the flame upwards at the outer rim to attach the flame to thelower plate.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional gas-fired water heater.

FIG. 2 is a perspective view of a low NOx burner.

FIG. 3 is a bottom view of the burner of FIG. 2.

FIG. 4 is a cross-section view of the burner taken along line 4-4 inFIG. 3.

FIG. 5 is an enlarged sectional view of a portion of the burner of FIG.4.

FIG. 6 is a perspective view of an alternative embodiment of a low NOxburner.

FIG. 7 is an enlarged view of a slot of the burner of FIG. 6.

FIG. 8 is an enlarged section view of a portion of the burner of FIG. 4.

FIG. 9 is a detail view of a portion of the burner of FIG. 2.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

FIG. 1 illustrates a water heater 100 including a tank 110 containingwater, a jacket 115 surrounding the tank 110, and a burner 120.Insulation 125 is provided between the tank 110 and the jacket 115. Aflammable fuel is provided to the burner 120 by a fuel line inlet 130connected to a fuel valve 135. The burner 120 is positioned in acombustion chamber 140 beneath the tank 110. The fuel valve 135 isconnected to a fuel supply. The fuel can be, for example, natural gas orpropane. The combustion chamber 140 is connected to an air supply, forexample, the atmosphere around the water heater 100. A flue tube 145extends from the combustion chamber 140 through the tank 110. Theproducts of combustion or exhaust gases created by the burner 120 flowthrough the flue tube 145 to heat the water stored in the tank 110. Abaffle (not shown) can be positioned in the flue tube 145 to increasethe heat transfer between the products of combustion and the waterstored in the tank 110. A cold water inlet pipe 150 is connected by aspud 155 to a dip tube 160 to supply cold water to the tank 110. A hotwater supply pipe 165 connected to a spud 170 supplies hot water to anend-use location, for example, a faucet. A temperature and pressure(T&P) valve 175 permits water to be released from the tank 110 in theevent of high pressure or high temperature within the tank 110. Otherthan the burner 120 to be described in detail below, the water heater100 as described above is a conventional gas-fired water heater 100.

FIG. 2 illustrates a low NOx pan burner 120 for use in a water heater100. The burner 120 includes an upper plate 180 and a lower plate 185joined together. The burner 120 defines a central axis or axis ofsymmetry 190. Upper, lower, above, below, inward, outward, and otherdirectional terms are relative to the central axis when the burner 120is in a normal operating position as shown in FIG. 1.

As shown in FIGS. 2 and 4, the upper plate 180 defines an upper plateaxis 195 that is collinear with the central axis 190 when the upperplate 180 is joined to the lower plate 185. The upper plate 180 includesan inner portion 200, a scalloped ridge 205, and a lip 210. The innerportion 200 extends radially outward from the upper plate axis 195 tothe scalloped ridge 205. As shown in FIG. 4, the scalloped ridge 205 islocated at a radial distance 207 from the upper plate axis 195. Thescalloped ridge 205 surrounds the inner portion 200 and definesalternating peaks 215 and valleys 220 (shown in FIG. 9) that are spacedequiangularly around the upper plate axis 195. As shown in FIG. 4, thelip 210 surrounds the inner portion 200. The lip 210 extends radiallyoutward from an upper portion 225 of the scalloped ridge 205 to an outercircumferential edge 230 of the upper plate 180. The lip 210 is angleddownwards from horizontal towards the lower plate 185. A lip angle 235is defined between the lip 210 and horizontal. The lip angle 235 canvary and is preferably twenty degrees or twenty-two degrees. The outercircumferential edge 230 is positioned at a radial distance 240 from theupper plate axis 195. The outer diameter of the upper plate 180 is lessthan the outer diameter of the lower plate 185.

As shown in FIGS. 2-4, the lower plate 185 defines a lower plate axis245 that is collinear with the central axis 190 when the lower plate 185is joined to the upper plate 180. The lower plate 185 includes an innerportion 250, a scalloped ridge 255, an exit portion 260, an intermediateportion 265, a trough 270, a transition 275, and an outer rim 280. Asshown in FIG. 3, the inner portion 250 includes a fuel/air intakeopening 285 and extends radially outward from the lower plate axis 245to the scalloped ridge 255. The scalloped ridge 255 is located at theradial distance 207 from the lower plate axis 245. The scalloped ridge255 surrounds the inner portion 250 and defines alternating peaks 290and valleys 295 (shown in FIG. 9) that are spaced equiangularly aroundthe lower plate axis 245. As shown in FIG. 3, the exit portion 260surrounds the inner portion 250. The exit portion 260 extends radiallyoutward from a lower portion 300 of the scalloped ridge 205 to a distalend 305. As shown in FIGS. 2 and 4, the exit portion 260 is angleddownward from the lower portion 300 of the scalloped ridge 205.

As shown in FIG. 4, the intermediate portion 265 surrounds the exitportion 260. The intermediate portion 265 extends from the distal end305 of the exit portion 260 to a distal end 310. The distal end 310 ofthe intermediate portion 265 is located at a radial distance 315 fromthe central axis 190. The radial distance 315 is greater than the radialdistance 240 so that the distal end 310 of the intermediate portion 265is radially outward from the outer circumferential edge 230 of the upperplate 180. The intermediate portion 265 defines a horizontal plane 320.

As shown in FIG. 5, the trough 270 surrounds the intermediate portion265 and is located below the intermediate portion 265. The trough 270 isplanar and has a radial width 325. The width 325 extends from a proximalend 330 of the trough 270 to a distal end 335 of the trough 270. Thewidth 325 can vary. The trough 270 is angled downwards from horizontal.The trough 270 is positioned at a trough angle 340 defined between thetrough 270 and the horizontal plane 320. The trough angle 340 can varyand is preferably is 1.2 degrees. Alternatively, the trough 270 ispositioned parallel to the horizontal plane 320. The entire trough 270is located below the horizontal plane 320. The transition 275 connectsthe intermediate portion 265 and the trough 270. The transition 275 ispositioned at an angle 345 from horizontal. The angle 345 can vary andcan be ninety degrees.

As shown in FIG. 5, the outer rim 280 surrounds the trough 270 andextends radially outward and upwards from the distal end 335 of thetrough 270 to an outer circumferential edge 350 of the lower plate 185.A rim angle 355 is defined between the outer rim 280 and the horizontalplane 320. The rim angle 355 can vary. Preferably, the rim angle 355 isgreater than the trough angle 340. An uppermost portion 360 of the outercircumferential edge 350 is positioned above the intermediate portion265. In one alternative, the uppermost portion 360 is even with theintermediate portion 265. In another alternative, the uppermost portion360 is below the intermediate portion 265. Alternatively, the burner 120does not include the trough 270 and the transition 275 so that the outerrim 280 extends radially outward and upward from the intermediateportion 265.

As shown in FIG. 4, the upper scalloped ridge 205 and the lowerscalloped ridge 255 are joined together such that a chamber 365 isdefined between the upper inner portion 200 and the lower inner portion250. As shown in FIG. 9, the peaks 215 of the upper scalloped ridge 205contact the peaks 290 of the lower scalloped ridge 255 to define aplurality of ports 370 between the valleys 220 of the upper scallopedridge 205 and the valleys 295 of the lower scalloped ridge 255. As shownin FIG. 3, the ports 370 extend radially outward from the chamber 365through the scalloped ridges 205, 255. As shown in FIG. 2, a bracket 375is coupled to the lower plate 185 for mounting the burner 120 in thecombustion chamber 140. A drain tube 380 extends through both plates180, 185.

As shown in FIG. 3, a plurality of first air apertures 385 are formedthrough the exit portion 260 radially outward from the ports 370 at adistance 390 from the central axis 190. A plurality of second airapertures 395 are formed through the exit portion 260 radially outwardfrom the first air apertures 385 at a distance 400 from the central axis190. The distance 400 is greater than the distance 390. Each first airaperture 385 is positioned in line with a port 370. Each second airaperture 395 is positioned between two adjacent ports 370 so each port370 is flanked by two adjacent second air apertures 395. The relativepositioning between the first air apertures 385 and the second airapertures 395 can vary. For example, in one alternative, each first airaperture 385 is positioned between two adjacent ports 370 and eachsecond air aperture 395 is positioned in line with a port 370. The sizeand shape of the first air apertures 385 and the second air apertures395 can vary. As illustrated, the first air apertures 385 and the secondair apertures 395 are circular holes.

As shown in FIG. 3, a plurality of third air apertures 405 are formedthrough the trough 270 at a distance 410 from the central axis 190. Thethird air apertures 405 are located radially outward from the second airapertures 395 and the distance 410 is greater than the distance 400.Each third air aperture 405 is positioned between a first air aperture385 and the adjacent second air aperture 395. The relative positioningbetween the first air apertures 385, the second air apertures 395, andthe third air apertures 405 can vary. The third air apertures 405 arepositioned near the transition 275. In one alternative, a portion ofeach third air aperture 405 extends into the transition 275. In a secondalternative, the third air apertures 405 are formed in the transition275. In a third alternative, the third air apertures 405 are formed inthe intermediate portion 265 near the trough 270. The size and shape ofthe third air apertures 405 can vary. As illustrated, the third airapertures 405 are circular holes.

In use, a fuel/air mixture is introduced to the chamber 365 through thefuel/air intake opening 285. As shown in FIG. 8, the fuel/air mixtureflows uniformly out of the chamber 365 through the ports 370 and iscombusted to create a diffuse flame 415. Secondary air is introduced tothe flame 415 through the first air apertures 385 and the second airapertures 395 to help complete combustion of the fuel/air mixture nearthe ports 370. The flame 415 is directed downwardly to a first elevationat the intermediate portion 265 by the lip 210 of the upper plate 180 sothat the flame 415 attaches to the intermediate portion 265. The flame415 is then directed downwards to a second elevation at the trough 270and attaches to the trough 270. The downward angle 345 of the trough 270helps to attach the flame 415 to the trough 270. Secondary air isintroduced to the flame 415 through the third air apertures 405 toassist in completing combustion of the fuel/air mixture near the trough270. The flame 415 is directed upwards out of the trough 270 by theouter rim 280. The change in the flame 415 direction at the outer rim280 also helps to attach the flame 415 to the trough 270.

The flame 415 attaches better to the lower plate 185 of the burner 120than a similar burner 120 with a lower plate that terminates at thedistal end of the intermediate portion. It is believed that thisimproved attachment of the flame 415 may be due to the changes indirection that the flame 415 undergoes as it moves from the intermediateportion 265 to the trough 270 and then to the outer rim 280.Alternatively, the improved attachment of the flame 415 may be due to anarea of low pressure in the trough 270 near the transition 275 thathelps to pull the flame 415 down into attachment with the trough 270.This area of low pressure would also help to draw secondary air throughthe third air apertures 405. Alternatively, the improved attachment ofthe flame 415 may be due to a change from laminar flow along theintermediate portion 265 to turbulent flow in the trough 270 near thetransition 275 and a change back to laminar flow further along thetrough 270 towards the outer rim 280. The outer rim 280 directs theflame 415 upward, unlike other similar burners that let the flame falloff of the outer circumferential edge of a planar lower plate. Thishelps to secure the flame 415 to the lower plate 185, directs the flame415 upwards towards the flue tube 145, and prevents heat damage to thecombustion chamber 140 and components attached to or near the combustionchamber 140.

The burner 120 is suited for uses of up to and including 50,000 BTU perhour. The burner 120 is especially suited for high-efficiency waterheaters that may include a near-condensing or less-than-fully-condensingheat transfer relationship between the products of combustion and thewater stored in the tank 110 and/or restricted air flow through the fluetube 145 due to baffling. Restricted air flow through the flue tube 145can make it difficult to sustain combustion at the burner 120. Thesecond air apertures 395 and the third air apertures 405 allow theburner 120 to sustain combustion even with restricted air flow. Thesecond air apertures 395 provide for higher entrainment of secondary airinto the flame at the port exit area. The third air apertures 405provide secondary air to support the flame in the trough 270.

The increased surface area of and amount of flame attachment to thelower plate 185 of the burner 120 as compared to a similar burner 120with a lower plate that terminates at the distal end of the intermediateportion allows for increased time for flame attachment to the lowerplate 185 and increased volume of the lower plate 185, which improvesthe ability of the lower plate 185 to function as a heat sink to lowerthe flame temperature. Lowering the flame temperature reduces theproduction of NOx. Therefore, the greater the width 385 of the trough270, the better performance of the burner 120 in terms of NOxproduction. Typically, the width 385 of the trough 270 is limited by thesize of the access opening to the combustion chamber 140 though whichthe burner 120 is installed. The trough 270 also improves the rigidityor stiffness of the lower plate 185. Alternatively, the lower plate 185can include a series of radial corrugations instead of or in addition tothe trough 270. The corrugations increase the surface area of the lowerplate 185 while also helping to improve the rigidity or stiffness of thelower plate 185.

FIG. 6 illustrates a burner 500 that is an alternative embodiment of theburner 120. The burner 500 is identical to the burner 120 except thatthe air apertures 385, 395, 405 are formed as elongated slots 420 ratherthan circular holes. As shown in FIG. 7, each slot 420 includes a majoraxis 425, an elongated portion 430, a leading end 435, and a trailingend 440. Each slot 420 extends along the major axis 425 from the leadingend 435 to the trailing end 440. Each major axis 425 extends radiallyfrom the central axis 190. In use, the slots 420 present secondary airto a radially longer portion of the flame than a circular hole. Thishelps to stretch out the introduction of the secondary air to the flameto increase the entrainment of the secondary air to the flame.

Various features and advantages of the invention are set forth in thefollowing claims.

1. A low NOx burner comprising: an upper plate defining an upper plateaxis and including an inner upper portion, an upper scalloped ridgesurrounding the upper inner portion, and a lip surrounding the upperscalloped ridge, the upper inner portion extending radially outward afirst radial distance from the upper plate axis to the upper scallopedridge, the upper scalloped ridge defining peaks and valleys and havingan upper portion, and the lip angling radially outward and downward fromthe upper portion of the upper scalloped ridge and defining an outercircumferential edge of the upper plate; and a lower plate defining alower plate axis and including a lower inner portion, a lower scallopedridge surrounding the lower inner portion, an exit portion surroundingthe lower scalloped ridge, an intermediate portion surrounding the exitportion, a trough surrounding the intermediate portion, and an outer rimsurrounding the trough, the inner portion having a fuel/air intakeopening and extending radially outward the first radial distance fromthe lower plate axis to the lower scalloped ridge, the lower scallopedridge defining peaks and valleys and having a lower portion, the exitportion angling radially outward and downward from the lower portion ofthe lower scalloped ridge, the intermediate portion extending from theexit portion to a distal end at a second radial distance, the secondradial distance greater than the first radial distance, the trough beingbelow and radially outward of the intermediate portion, the outer rimincluding an outer circumferential edge of the lower plate; wherein theupper scalloped ridge and the lower scalloped ridge are joined togetherso that the upper plate axis and the lower plate axis are collinear,such that a chamber is defined between the upper inner portion and thelower inner portion, such that the peaks of the upper and lowerscalloped ridges are in contact, and such that a plurality of ports aredefined between the valleys of the upper and lower scalloped ridges, theports extending radially outward from the chamber through the scallopedridges; wherein the chamber is adapted to receive a fuel/air mixturethrough the fuel/air intake opening; wherein the ports are adapted topermit a flow of the fuel/air mixture from the chamber for combustion tocreate a diffuse flame; wherein the intermediate portion is positionedsuch that the flame attaches to the intermediate portion; wherein theintermediate portion and trough are arranged such that flame is directeddownwards to the trough from the intermediate portion and attaches tothe trough; and wherein the outer rim is positioned and angled to attachthe flame to the trough and to direct the flame upwards from the trough.2. The low NOx burner of claim 1, wherein the intermediate portiondefines a horizontal plane; wherein the entire trough is located belowthe horizontal plane; wherein the trough is angled downwards withrespect to the horizontal plane; and wherein a trough angle is definedbetween the horizontal plane and the trough.
 3. The low NOx burner ofclaim 2, wherein a rim angle is defined between the outer rim and thehorizontal plane; and wherein the rim angle is greater than the troughangle.
 4. The low NOx burner of claim 2 further comprising: a pluralityof first air apertures in the lower plate, the first air apertureslocated radially outward from the ports; and a plurality of second airapertures in the lower plate, the second air apertures located radiallyoutward from the first air apertures; wherein the first air aperturesand the second air apertures are positioned near the ports to introducesecondary air to help to complete combustion of the fuel/air mixture. 5.The low NOx burner of claim 4 further comprising: a plurality of thirdair apertures in the lower plate, the third air apertures locatedradially outward from the second air apertures; wherein the third airapertures are positioned to introduce secondary air near the trough tohelp complete combustion of the fuel/air mixture.
 6. The low NOx burnerof claim 5, wherein the third air apertures are in the trough.
 7. Thelow NOx burner of claim 6, wherein the first air apertures are formed asslots, the second air apertures are formed as slots, and the third airapertures are formed as slots.
 8. The low NOx burner of claim 6, whereinthe first air apertures are formed as circular holes, the second airapertures are formed as circular holes, and the third air apertures areformed as circular holes.
 9. The low NOx burner of claim 2 furthercomprising: a plurality of air apertures in the trough; wherein the airapertures are positioned to introduce secondary air near the trough tohelp to complete combustion of the fuel/air mixture.
 10. The low NOxburner of claim 1 further comprising: a plurality of first air aperturesin the lower plate, the first air apertures located radially outwardfrom the ports; and a plurality of second air apertures in the lowerplate, the second air apertures located radially outward from the firstair apertures; wherein the first air apertures and the second airapertures are positioned near the ports to introduce secondary air tohelp to complete combustion of the fuel/air mixture.
 11. The low NOxburner of claim 10 further comprising: a plurality of third airapertures in the lower plate, the third air apertures located radiallyoutward from the second air apertures; wherein the third air aperturesare positioned to introduce secondary air near the trough to helpcomplete combustion of the fuel/air mixture.
 12. The low NOx burner ofclaim 11, wherein the third air apertures are in the trough.
 13. The lowNOx burner of claim 1 further comprising: a plurality of air aperturesin the trough; wherein the air apertures are positioned to introducesecondary air near the trough to help complete combustion of thefuel/air mixture.
 14. A low NOx burner comprising: an upper platedefining an upper plate axis and including an inner upper portion, anupper scalloped ridge surrounding the upper inner portion, and a lipsurrounding the upper scalloped ridge, the upper inner portion extendingradially outward a first radial distance from the upper plate axis tothe upper scalloped ridge, the upper scalloped ridge defining peaks andvalleys and having an upper portion, and the lip angling radiallyoutward and downward from the upper portion of the upper scalloped ridgeand defining an outer circumferential edge of the upper plate; and alower plate defining a lower plate axis and including a lower innerportion, a lower scalloped ridge surrounding the lower inner portion, anexit portion surrounding the lower scalloped ridge, an intermediateportion surrounding the exit portion and an outer rim surrounding theintermediate portion, the inner portion having a fuel/air intake openingand extending radially outward the first radial distance from the lowerplate axis to the lower scalloped ridge, the lower scalloped ridgedefining peaks and valleys and having a lower portion, the exit portionangling radially outward and downward from the lower portion of thelower scalloped ridge, the intermediate portion extending from the exitportion to a distal end at a second radial distance, the second radialdistance greater than the first radial distance, the outer rim includingthe an outer circumferential edge of the lower plate; wherein the upperscalloped ridge and the lower scalloped ridge are joined together sothat the upper plate axis and the lower plate axis are collinear, suchthat a chamber is defined between the upper inner portion and the lowerinner portion, such that the peaks of the upper and lower scallopedridges are in contact, and such that a plurality of ports are definedbetween the valleys of the upper and lower scalloped ridges, the portsextending radially outward from the chamber through the scallopedridges; wherein the chamber is adapted to receive a fuel/air mixturethrough the fuel/air intake opening; wherein the ports are adapted topermit a flow of the fuel/air mixture from the chamber for combustion tocreate a diffuse flame; wherein the intermediate portion is positionedsuch that the flame attaches to the intermediate portion; and whereinthe outer rim is positioned and angled to attach the flame to the lowerplate and to direct the flame upwards from the lower plate.
 15. The lowNOx burner of claim 14 further comprising: a plurality of first airapertures in the lower plate, the first air apertures located radiallyoutward from the ports; and a plurality of second air apertures in thelower plate, the second air apertures located radially outward from thefirst air apertures; wherein the first air apertures and the second airapertures are positioned near the ports to introduce secondary air tohelp to complete combustion of the fuel/air mixture.
 16. A method ofoperating a low NOx burner, the method comprising the steps of:providing a low NOx burner including an upper plate having an outerdiameter and a lower plate having an outer rim and an outer diameter,the plates joined together to define a chamber and a plurality of portsformed between the plates, the ports extending radially outward from thechamber, and the outer diameter of the upper plate being less than theouter diameter of the lower plate; providing a fuel/air mixture to thechamber; directing the fuel/air mixture through the ports; combustingthe fuel/air mixture to create a flame; and directing the flame upwardsat the outer rim to attach the flame to the lower plate.
 17. The methodof claim 16, further comprising: directing the flame from the ports to afirst elevation on the lower plate below the ports to attach the flameto the lower plate at the first elevation; and directing the flame fromthe first elevation to a second elevation on the lower plate below thefirst elevation to attach the flame to the lower plate at the secondelevation.
 18. The method of claim 17, the method further comprising:providing a first portion of secondary air to the flame at a firstdistance radially outward from the ports; and providing a second portionof secondary air to the flame at a second distance radially outward fromthe ports, the second distance greater than the first distance.
 19. Themethod of claim 18, the method further comprising: providing a thirdportion of secondary air to the flame at a third distance radiallyoutward from the ports, the third distance greater than the seconddistance; providing the third portion of secondary air at the secondelevation.
 20. The method of claim 17, the method further comprising:providing secondary air to the flame radially outward from the ports atthe second elevation.